1. Field of the Invention
The present invention disclosed herein relates to semiconductor devices, and more particularly, to an integrated circuit cards having condition detectors.
2. Description of the Related Art
A smart card includes an embedded microprocessor and a memory, or includes a memory without a logic unit. A microprocessor card is able to add, erase and process data, but a memory chip card (e.g., a prepaid phone card) is able to perform only certain predetermined functions. Unlike a magnetic strip card, a smart card internally executes and processes all required functions and information, and thus does not need to access a remote database. Nowadays, smart cards are rapidly developing with new markets and applications, and may be generally classified into three types: integrated circuit (IC) microprocessor cards, IC memory cards and optical memory cards.
With recent implementation of electronic funds transactions and financial services, the stability and security of chips in an electronic apparatus are becoming increasing important. Insufficient stability and security may cause data to be improperly stored. Experiments evaluating chip stability and security may be performed by varying external factors. For example, surge or ripple components may be added to an external power source voltage. The stability and security of the chip may be also evaluated by rapidly varying a frequency of an external clock, or an external temperature.
In a normal mode, chip signals are affected by various internal and external factors. The most significant signal is an address/data signal transferred between a processing unit and a memory. Potential harmful effects on address/data signals due to internal and external factors are discussed below.
Referring to FIG. 1, which shows a normal timing operation of an IC card, a valid address is obtained from a processing unit at a rising edge of a clock signal. The processing unit must therefore provide a stable address before a rising edge of the clock signal. In the normal mode, data corresponding to the valid address may be provided to the processing unit from a memory. Otherwise, as illustrated in FIG. 2, if a frequency f2 is higher than a normal frequency f1, the memory (and/or peripheral devices) will obtain an address on a bus before the processing unit loads a valid address into the bus based on the time of the rising edge of the higher frequency clock signal. The address obtained by the memory will therefore be invalid and may result in a malfunction of the chip. In another case, as illustrated in FIG. 3, the processing unit may be late in outputting an address, e.g., because of degradation in functions (or drivabilities) of transistors in the processing unit. Therefore, although the clock signals operate in the same frequency (f1), the memory may obtain an invalid address. As a result, a malfunction may occur in the chip.
When operational conditions of a chip change due to external factors, a processing unit may be initialized (or re-initialized) to prevent chip malfunction. The initialization provides chip security. However, the chip may be initialized even when the operational environments vary rapidly under hacking or otherwise unstable conditions. Such variations in the external environment may cause degradation of chip stability during the initialization.